A Manhattan couple and their toddler decide to live for a year without toilet paper, dis posable diapers or a fridge, composting their waste in a box full of worms they keep in their living room. We are fortunate that the resulting documentary “No Impact Man” is not presented in smell-o-vision.

Colin Beavan, the writer who trademarked the title and turned it into a book and blog, has proved a master of publicity even as he finds himself lashed by fellow liberals angry either that they didn’t think of such a meaningless but profitable stunt or that he’s making them feel guilty about not going to such extremes. (Beavan, who vowed to eat only locally grown food, carries around a germy Mason jar from which he drinks all his liquids.) From his Fifth Avenue co-op, he makes an amusing specimen of the earnest eco-dweeb.

This spongy porridge eater reminded me that only a couple of letters separate locavore from loco bore. But the hero of the piece (for a while, until she is converted) is his cheerful, relatively normal wife, Michelle Conlin, who confesses to sneaking ice from the office refrigerator (she works at Business Week) and is dying for a cup of coffee (sorry: not locally grown).

She continues to wear makeup throughout, just as he installs a solar panel that provides just enough juice to fire up his computer, because vanity is harder to kill than America’s SUV habit.

The film makes little sense (the couple refuses to ride subways, but Metro-North is OK), but it’s a diverting conversation piece/freak show. It skips over some sticky issues. There is a hint, for instance, that the daughter is not pleased to grow up amid flies instead of Froot Loops. A highly emotional moment isn’t captured on film but merely referred to in the past tense. Also, we never learn what the family does in lieu of toilet paper.

Let’s hope no-impact living catches on; any fad that involves submitting to germ rule and riding bikes in heavy traffic is bound to be as self-nullifying as a suicide cult, leaving lots of yummy natural resources for you and me to enjoy. Green yuppies — the guppies — even feel guilty about reproducing. They’re pedaling to extinction.

Meanwhile, the daughter, deprived of TV, cold milk and even out-of-season produce, seems destined to grow up somewhere to the right of Ayn Rand. I can’t wait for her memoir about living in a permanent Lent. At least Catholics have God instead of Gore, though.